Method and Apparatus for Producing Power and Hydrogen

ABSTRACT

Both power and H 2  are produced from a gaseous mixture, comprising H 2  and CO 2 , using first and second pressure swing adsorption (PSA) systems in series. The gaseous mixture is fed at super-atmospheric pressure to the first PSA system, which comprises adsorbent that selectively adsorbs CO 2  at said pressure, and CO 2  is adsorbed, thereby providing an H 2 -enriched mixture at super-atmospheric pressure. A fuel stream is formed from a portion of the H 2 -enriched mixture, which is combusted and the combustion effluent expanded to generate power. Another portion of the H 2 -enriched mixture is sent to the second PSA system, which comprises adsorbent that selectively adsorbs CO 2  at super-atmospheric pressure, and CO 2  is adsorbed, thereby providing a high purity H 2  product. In preferred embodiments, the division of H 2 -enriched mixture between forming the fuel stream and being fed to the second PSA system is adjustable.

BACKGROUND OF THE INVENTION

The present invention relates to methods and apparatus for producingpower and hydrogen (H₂) from a gaseous mixture comprising H₂ and carbondioxide (CO₂), and in particular for concurrently and/or adjustablyproducing electric power and a high purity hydrogen product (preferablyhaving a purity of at least about 99.9 mole %, more preferably at leastabout 99.99 mole %) from a gaseous mixture obtained from gasification ofor from reforming a carbonaceous feedstock.

Gasification of a solid or liquid carbonaceous feedstock, or partialoxidation or steam methane reforming of a gaseous or liquid carbonaceousfeedstock, followed by subsequent separation of hydrogen from thegasifier or reformer effluent, is a well known technique of producinghydrogen, and has been a topic of research and development for manyyears. As is also known, the separated hydrogen product may then be putto a number of uses, depending on its purity. For example, hydrogen maybe used as a fuel in for example a gas turbine, thereby generating power(in particular electric power), and/or it may be used in refinery,chemicals and/or fuel cell applications. Where the hydrogen product isto be used as a fuel for a gas turbine for generating power, a somewhatlower purity is typically acceptable than that which is required wherethe hydrogen product is intended for refinery, chemicals or fuel cellapplications (all of which typically require an H₂ purity of at least99.9 mole %, and more typically at least 99.99 mole %).

Gasifier or reformer effluent typically comprises H₂, CO₂ and carbonmonoxide (CO) as the major components, with minor amounts of othercomponents such as methane (CH₄), ammonia (NH₃), nitrogen (N₂), argon(Ar) and, where the feedstock contained sulphur, certain sulphurcontaining species (predominantly hydrogen sulphide (H₂S), but otherspecies such as carbonyl sulphide (COS) and carbon disulphide (CS₂) mayto a lesser extent also be present). This effluent is often thensubjected to a water-gas-shift reaction to convert, by reaction withH₂O, some or all of the CO to CO₂ and H₂. In circumstances where anysulphur containing species are not first removed by appropriate sorptivetechniques (as may be necessary where a sulphur sensitive shift catalystis to be used) this can have the side-effect of also increasing theconcentration of H₂S in the shifted mixture, due to conversion of othersulphur species in the crude syngas stream to H₂S during thewater-gas-shift reaction.

If an H₂ product suitable for use as a fuel for generating power or foruse in refinery, chemicals or fuel cell applications is desired, furtherseparation of the H₂ from the other components of the gasifier, reformeror shift-converter effluent will typically then be required. An array oftechnologies for the separation of H₂ from such mixtures, and from othermixtures comprising H₂ and CO₂, have been developed and are known. Oneapproach is to utilize pressure swing adsorption (PSA), and a variety ofmethods adopting this approach have been described in the art.

For example, US-A1-2007/0178035 describes a method of treating a gaseousmixture, such as obtained from a gasification process, comprising H₂,CO₂ and one or more combustible gases (i.e. H₂S, CO and CH₄). H₂ isseparated, preferably by pressure swing adsorption (PSA), from thegaseous mixture to produce a separated high purity H₂ gas and a crudeCO₂ gas comprising the combustible gases. The crude CO₂ gas is combustedto produce heat and a CO₂ product gas comprising the combustion productsof the combustible gas(es). Heat is recovered from the CO₂ product gasby indirect heat exchange with the H₂ gas, to which a diluent (e.g. N₂or H₂O) may have been added, and the warmed H₂-containing gas may thenbe fed as fuel to a gas turbine. Where the combustion product(s)comprise SO_(x) (SO₂ and SO₃), these may be removed by a process thatinvolves washing the gas with water and maintaining the gas at elevatedpressure.

U.S. Pat. No. 4,171,206 describes a method in which two PSA systems,each comprising a plurality of adsorbent beds operating in parallel, areused in series to separate a high purity H₂ product and a CO₂ productfrom a feed gas comprising H₂ and CO₂ and one or more dilute components,such as CO and CH₄. The feed gas may for example be produced from ashift converter in a hydrocarbon reforming plant. The feed gas is fed tothe first PSA system at super-atmospheric pressure, and CO₂ is adsorbed.The unadsorbed gas pushed through the first PSA system is then fed tothe second PSA system where the dilute components are adsorbed, and theunadsorbed gas pushed through the second PSA system is withdrawn as highpurity H₂ product. The first PSA system employs a vacuum pressure swingadsorption process, whereby the desorbed gas obtained at ambient andsub-ambient pressures during blowdown and evacuation of the beds of thefirst PSA system is withdrawn as high purity CO₂ product. The desorbedgas obtained at about ambient pressure during blowdown/purging of thebeds of the second PSA system is withdrawn as a product containing H₂,CO and CH₄ and having good fuel value.

U.S. Pat. No. 4,790,858, U.S. Pat. No. 4,813,980, U.S. Pat. No.4,836,833, U.S. Pat. No. 5,133,785 describe a number of modifications toor variations on the method described in U.S. Pat. No. 4,171,206. U.S.Pat. No. 4,790,858 describes a method in which the product containingH₂, CO and CH₄ obtained at atmospheric pressure from the second PSAsystem is compressed and fed to a third PSA system, so as to recoversome of the H₂ present in said feed as further high purity H₂ product.U.S. Pat. No. 4,813,980 describes the use of first and second PSAsystems to separate a reformer off-gas, comprising H₂, N₂, CO₂ and minorquantities of CH₄, CO and Ar, into a high purity ammonia synthesis gas(e.g. a product comprising a 3:1 ratio of H₂ to N₂), a high purity CO₂product, and a product containing H₂, CH₄ and CO that can be used asfuel for the reformers. U.S. Pat. No. 4,836,833 describes a method inwhich the feed to the first PSA system is the reformate from a steammethane reformer, and the desorbed product obtained from the second PSAsystem contains CO, H₂ and minor amounts of CH₄ and is further separatedin a multi-membrane system to obtain a high purity CO product. U.S. Pat.No. 5,133,785 describes certain modifications to the PSA cycle describedin U.S. Pat. No. 4,171,206 for operation of the first and second PSAsystems.

U.S. Pat. No. 3,102,013 discloses a method of separating a mixture of atleast three components, designated A, B and C, using at least two PSAbeds in series. The mixture is fed to the first bed at high pressure,where component C is adsorbed, and the unadsorbed gas pushed through thefirst bed is fed to the second bed, where component B is selectivelyadsorbed, thereby obtaining a product comprising component A. A portionof this product is used to purge the beds at low pressure. The gaspurged from the first bed comprises components A and C and the gaspurged from the second bed comprises components A and B. These purgedgases are then separated in further separation beds into components Aand C and A and B, respectively.

U.S. Pat. No. 4,042,349 discloses methods of separating mixtures usingtwo or more PSA beds in series and/or in parallel. In one embodiment twobeds are used in series, and in parallel with two further beds inseries, to separate an H₂ stream from a feed mixture comprising H₂, N₂,CH₄, Ar and NH₃.

U.S. Pat. No. 4,539,020 discloses a method of separating CO from a feedgas comprising CO₂, CO and a less adsorbable component than CO, such asN₂, H₂ or CH₄, through PSA using in series at least two adsorbent beds.The first bed selectively adsorbs CO₂ from the feed gas, and the CO₂depleted gas pushed through the first bed is fed to the second bed whichselectively adsorbs CO. The gas pushed through the second bed comprisesCO and the less adsorbable components and can be used for purging thefirst bed, with the remainder being usable as a fuel in view of itsconsiderable CO content. The gas evacuated from the second bed undervacuum forms the high purity CO product. In one example, the process isused to separate a gaseous mixture comprising CO, CO₂, N₂, H₂ and O₂which is an off-gas from a converter furnace.

U.S. Pat. No. 4,696,680 describes a method for bulk separation of agaseous mixture, comprising predominantly H₂, CO, CH₄, CO₂ and H₂S,derived from the gasification of coal. In one embodiment, the gaseousmixture is fed at about atmospheric pressure to a first PSA bed whichselectively adsorbs CO₂ and H₂S. The non-adsorbed gas, which comprisesH₂, CO and CH₄, from the first PSA bed is compressed and fed to a secondPSA bed at a pressure at which H₂, CO and CH₄ are all adsorbed. Thepressure in the second PSA bed is then gradually decreased tosequentially desorb a high purity H₂ product, a CO enriched product anda CH₄ enriched product. The first PSA bed is regenerated by desorbingthe CO₂ and H₂S at sub-atmospheric pressure. The CO and CH₄ enrichedproducts may be utilized as a mixture for providing fuel gas.

U.S. Pat. No. 4,761,167 describes a method of removing N₂ from a fuelgas stream comprising CH₄, N₂ and CO₂. The fuel gas stream is fed to aPSA system, comprising a plurality of adsorbent beds employed inparallel that selectively adsorb CO₂ from a mixture. The unsorbedeffluent, consisting substantially of CH₄ and N₂, exiting the PSA systemis then fed to a Nitrogen Rejection Unit (NRU) that separates the N₂from the CH₄ by fractional distillation. The nitrogen stream obtainedfrom the NRU can then be used for purging the beds of the PSA systemduring regeneration of the beds at atmospheric pressure.

US-B1-6340382 describes the design and operation of a PSA system forproducing a high purity (≧99.9%) H₂ product from a gas stream containingmore than about 50 mole % H₂, such as streams that contain from 60 to 90mole % H₂ and include CO₂, H₂O, CH₄, N₂ and CO. The document alsocross-references a number of previous works on PSA cycles and adsorbentoptions for producing high purity H₂.

US2007/0199446 describes a vacuum pressure swing adsorption (VPSA)process for producing an essentially CO-free hydrogen gas stream from ahigh-purity, e.g. pipeline grade, hydrogen gas stream using one or twoadsorber beds. The high-purity hydrogen gas stream consists of about99.9% by volume H₂ with up to about 1000 ppm of non-hydrogen impurities,and the essentially CO-free hydrogen gas stream contains less than 1 ppmCO. The PSA process uses physical adsorbents with high heats of nitrogenadsorption, intermediate heats of carbon monoxide adsorption, and lowheats of hydrogen adsorption, and uses vacuum purging, high feed streampressures (e.g. feed pressures of as high as around 1,000 bar (100 MPa))and feed times of greater than around 30 minutes to produce theessentially CO-free hydrogen from the pipeline grade hydrogen.

US-A1-2007/0227353 describes a method of separating a CO₂ product havinga purity of at least 80 mole % from a feed stream containing at leastCO₂ and H₂ via VPSA. The feed may for example be a syngas stream,obtained from steam methane reforming and shift-converting natural gas,which is fed to the VPSA unit at super-atmospheric pressure. TheH₂-enriched unsorbed effluent is sent to a second PSA unit where it isfurther separated to obtain high-pressure, high purity H₂ product. Thegas desorbed from the VPSA unit at sub-atmospheric pressure is withdrawnas the CO₂ product, and the gas desorbed from the second PSA unit may beused as a fuel stream for the steam methane reformer.

US-B2-7550030 and US-A1-2008/0072752 describe variations on the methoddescribed in US-A1-2007/0227353. In the method of US-B2-7550030, a thirdstream is obtained from the VPSA unit, which stream is an H₂-depletedstream (relative to the feed to the VPSA unit) which is formed from gasdesorbed from the beds of the VPSA during depressurization of the bedsprior to evacuation of the beds at sub-atmospheric pressure. ThisH₂-depleted stream may then be mixed with gas desorbed from the secondPSA unit, to form a combined fuel stream for the steam methane reformer,or may be sent to an incinerator or vented. In the method ofUS-A1-2008/0072752, a stream formed from gas desorbed from the beds ofthe VPSA unit during depressurization of the beds prior to evacuation ofthe beds at sub-atmospheric pressure is recycled into the fresh feed tothe VPSA unit.

WO2005/118126 describes a method of producing high purity hydrogen, inwhich a hydrocarbon feed is reformed at high pressure in apartial-oxidation or steam-methane reformer to produce a high pressureeffluent containing H₂ which is separated in a PSA unit to produce ahigh purity product stream (i.e. 98 volume % H₂ or higher). The H₂containing gas purged from the PSA unit may be combusted to heat thefeed air to the reformer. Where the hydrocarbon feed is a sour feed(i.e. contains H₂S), an H₂S sorber, containing for example a sorbentsuch as zinc oxide, may be used to remove H₂S from the reformer effluentprior to separation in the PSA unit.

FR2899890 describes a PSA process for producing a H₂ product (98-99.5mole % purity) from a feed gas containing hydrogen, in which the gasused to purge the beds of the PSA unit during the purge step of the PSAprocess is an H₂ rich gas which is at least partly obtained from anexternal source, such as from a petrochemical or oil unit in an oilrefinery.

It is an objective of preferred embodiments of the present invention toprovide efficient and flexible production of both power and hydrogenfrom a gaseous mixture comprising H₂ and CO₂, such as for example amixture obtained from gasification of or reforming hydrocarbonfeedstock.

Operation of a plant to make both a high purity H₂, for example forselling to a customer, and a lower purity H₂ stream for use as a fuelfor making power by combustion in, for example, a gas turbine, can bedesirable for a number of reasons. In particular, having the capabilityto make both electric power and high purity H₂ has the potential forsignificant cost advantages. Due to economies of scale, the incrementalcapital and operating cost of making power alongside high purity H₂ ispotentially significantly less than that for making the same amount ofpower and/or high purity H₂ in standalone plants.

There can also be advantages in having the flexibility to varyproduction between a high purity H₂ for sale and a lower purity H₂ foruse as a fuel for making power. For example, the price of electric powercan vary considerably, with peaks and troughs in demand depending uponfactors such as the time of the day or the season. There could thereforebe commercial benefit in being able to turn down or turn off gasturbines when the price of electric power is low and ramp up theproduction of high purity H₂ when it can be sold at a higher price thanpower. Likewise, when the price of electric power is high it could becommercially beneficial to be able reduce or halt production of highpurity H₂ in order to increase production of electric power.

In addition, there may be circumstances in which the source of thegaseous mixture (from which both power and H₂ are to be produced) cannotbe completely relied upon. For example, in circumstances where thegaseous mixture is obtained from gasification of a carbonaceousfeedstock by several gasifiers, it may be that one or more gasifiers,which are known to be somewhat unreliable, suddenly and unexpectedlyfail during normal operation. Where the plant ordinarily produces bothpower and high purity H₂ and has the ability to vary production of thesame, the plant operator may at least have the option of reducing orceasing production of power or high purity H₂ in order that desiredlevels of production of the other are maintained. For example, wherehigh purity H₂ is required for continuous supply to a customer, theability to maintain the level of supply to the customer by, ifnecessary, reducing or halting (at least temporarily) power productioncan provide the customer with a more reliable service.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda method for concurrently producing power and H₂ from a gaseous mixturecomprising H₂ and CO₂, the method comprising:

feeding the gaseous mixture at super-atmospheric pressure to a firstpressure swing adsorption (PSA) system comprising adsorbent thatselectively adsorbs CO₂ at said pressure, and selectively adsorbing CO₂from the gaseous mixture with said adsorbent and at said pressure,thereby obtaining an H₂-enriched mixture at super-atmospheric pressure;

forming a fuel stream from a portion of the H₂-enriched mixture,combusting said fuel stream and expanding the resulting combustioneffluent to generate power; and

feeding another portion of the H₂-enriched mixture at super-atmosphericpressure to a second PSA system comprising adsorbent that selectivelyadsorbs CO₂ at said pressure, and selectively adsorbing CO₂ from saidportion of the H₂-enriched mixture with said adsorbent and at saidpressure, thereby obtaining an H₂ product.

According to a second aspect of the present invention, there is provideda method for adjustably producing either or both of power and H₂ from agaseous mixture comprising H₂ and CO₂, the method comprising:

feeding the gaseous mixture at super-atmospheric pressure to a firstpressure swing adsorption (PSA) system comprising adsorbent thatselectively adsorbs CO₂ at said pressure, and selectively adsorbing CO₂from the gaseous mixture with said adsorbent and at said pressure,thereby obtaining an H₂-enriched mixture at super-atmospheric pressure;and

forming either or both of a fuel stream and a PSA feed stream from theH₂-enriched mixture, the fuel stream being combusted and the resultingcombustion effluent expanded to generate power, and the PSA feed streambeing fed at super-atmospheric pressure to a second PSA systemcomprising adsorbent that selectively adsorbs CO₂ at said pressure, CO₂being selectively adsorbed from said PSA feed stream with said adsorbentand at said pressure, to thereby obtain an H₂ product;

wherein the division of H₂-enriched mixture between the fuel stream andPSA feed stream is adjustable, thereby allowing the proportion of theH₂-enriched mixture used to form the fuel stream to be increased byreducing the proportion used to form the PSA feed stream, andvice-versa, without halting the feed of the gaseous mixture to the firstPSA system.

According to a third aspect of the present invention, there is providedan apparatus for producing power and H₂ from a gaseous mixturecomprising H₂ and CO₂, the apparatus comprising:

a first pressure swing adsorption (PSA) system, comprising adsorbentthat selectively adsorbs CO₂ at super-atmospheric pressure;

a conduit arrangement for feeding at super-atmospheric pressure thegaseous mixture into the first PSA system;

a gas turbine for combusting a fuel stream and expanding the resultingcombustion effluent to generate power;

a second PSA system, comprising adsorbent that selectively adsorbs CO₂at super-atmospheric pressure;

a conduit arrangement for withdrawing at super-atmospheric pressure anH₂-enriched mixture from the first PSA system, introducing a fuel streaminto the gas turbine formed from a portion of said H₂-enriched mixture,and introducing another portion of said H₂-enriched mixture into thesecond PSA system; and

a conduit arrangement for withdrawing an H₂ product from the second PSAsystem.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a flow sheet depicting an embodiment of the present invention;

FIG. 2A is a flow sheet depicting another embodiment of the presentinvention in a first mode of operation; and

FIG. 2B is a flow sheet depicting the embodiment of FIG. 2A in a secondmode of operation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides in one aspect a method for concurrentlyproducing power and H₂ from a gaseous mixture comprising H₂ and CO₂, themethod comprising:

feeding the gaseous mixture at super-atmospheric pressure to a firstpressure swing adsorption (PSA) system comprising adsorbent thatselectively adsorbs CO₂ at said pressure, and selectively adsorbing CO₂from the gaseous mixture with said adsorbent and at said pressure,thereby obtaining an H₂-enriched mixture at super-atmospheric pressure;

forming a fuel stream from a portion of the H₂-enriched mixture,combusting said fuel stream and expanding the resulting combustioneffluent to generate power; and

feeding another portion of the H₂-enriched mixture at super-atmosphericpressure to a second PSA system comprising adsorbent that selectivelyadsorbs CO₂ at said pressure, and selectively adsorbing CO₂ from saidportion of the H₂-enriched mixture with said adsorbent and at saidpressure, thereby obtaining an H₂ product.

As will be discussed in further detail, this arrangement, in which twoPSA systems are used in series to separate an H₂ product from thegaseous mixture, with a portion of the intermediate H₂-enriched mixtureobtained at super-atmospheric pressure from the first PSA system beingused to form a fuel stream for generating power, provides an efficientmeans of generating both power and a high purity H₂ product. Inparticular, this arrangement provides efficiency benefits as compared toalternative arrangements that might be conceived using a single PSAsystem, two PSA systems in parallel, or two PSA systems in series withthe fuel stream being alternatively formed.

In preferred embodiments of the invention, the division of H₂-enrichedmixture between forming the fuel stream and being fed to the second PSAsystem is adjustable, thereby allowing the proportion of the H₂-enrichedmixture used to form the fuel stream to be increased by reducing theproportion fed to the second PSA system, and vice-versa, without haltingthe feed of the gaseous mixture to the first PSA system. This providesfurther benefits in terms of providing flexibility between the levels ofproduction of power and H₂ product.

The present invention also provides, in another aspect, a method foradjustably producing either or both of power and H₂ from a gaseousmixture comprising H₂ and CO₂, the method comprising:

feeding the gaseous mixture at super-atmospheric pressure to a firstpressure swing adsorption (PSA) system comprising adsorbent thatselectively adsorbs CO₂ at said pressure, and selectively adsorbing CO₂from the gaseous mixture with said adsorbent and at said pressure,thereby obtaining an H₂-enriched mixture at super-atmospheric pressure;and

forming either or both of a fuel stream and a PSA feed stream from theH₂-enriched mixture, the fuel stream being combusted and the resultingcombustion effluent expanded to generate power, and the PSA feed streambeing fed at super-atmospheric pressure to a second PSA systemcomprising adsorbent that selectively adsorbs CO₂ at said pressure, CO₂being selectively adsorbed from said PSA feed stream with said adsorbentand at said pressure, to thereby obtain an H₂ product;

wherein the division of H₂-enriched mixture between the fuel stream andPSA feed stream is adjustable, thereby allowing the proportion of theH₂-enriched mixture used to form the fuel stream to be increased byreducing the proportion used to form the PSA feed stream, andvice-versa, without halting the feed of the gaseous mixture to the firstPSA system.

Accordingly, in this method both power and an H₂ product can, again, besimultaneously produced by separating the starting gaseous mixture,comprising H₂ and CO₂, using two PSA systems in series, therebyproviding the aforementioned benefits in terms of process efficiency.However, in this method the division of H₂-enriched mixture between thefuel stream and PSA feed stream is fully adjustable, without halting thefeed of the gaseous mixture to the first PSA system, such that at anyone point in time the method may be operated so as to generate solelypower or generate solely H₂ product. This, of course, maximizes theflexibility of the process.

In the methods according to the present invention, the gaseous mixturefed to the first PSA system comprises, as noted above, H₂ and CO₂.Preferably H₂ and CO₂ constitute the major components of the mixture(i.e. the mole % of each of these components individually is greaterthan that of any other individual component present in the mixture).Preferably, the mixture comprises: about 20 to 90% mole %, morepreferably about 30 to 75 mole %, H₂; and about 10 to 60% mole % CO₂.

The gaseous mixture maycomprise other components in addition to H₂ andCO₂. For example, the gaseous mixture may further comprise: othercarbonaceous components, such as CO, CH₄, and/or longer chainhydrocarbons; sulphurous components, such as H₂S, COS and/or othersulphides (of which H₂S will typically be the major component, i.e.present in a mole % that is greater than that of any other individualsulphurous component); one or more inert gases, such as N₂ and/or Ar;and/or water. In preferred embodiments the mixture further comprisesH₂S. Where H₂S is present, this is preferably present in an amount of upto about 4 mole %, more preferably up to about 2 mole %. Where CO ispresent, it is preferably present in an amount of no more than 10 mole%. Where CH₄ is present, it is preferably present in an amount of nomore than 10 mole %.

Preferably, the gaseous mixture is obtained from gasification of orreforming carbonaceous feedstock. The carbonaceous feedstock may, forexample, be a carbon-rich (e.g. coal) or hydrocarbon (e.g. natural gas)feedstock. If there is sulphur in the feedstock (such as where thefeedstock is coal or petcoke) then this will typically result in thepresence of one or more of the aforementioned sulphurous components inthe gaseous mixture. Any inert gases such as N₂ and Ar present in thegaseous mixture would typically come from the fuel or the oxidant (e.g.about 95% purity O₂ from an air separation unit) used forgasification/reforming. The gaseous mixture obtained fromgasification/reforming may also have been subjected to one or morewater-gas-shift reaction steps, whereby at least some of the CO presentin the initial effluent from the gasifier/reformer has been converted byreaction with H₂O to obtain further H₂ and CO₂. Water may thus bepresent in the gaseous mixture as a result of the initialgasification/reforming process, as a result of subsequent shift reactionsteps, and/or as a result of other forms of processing of the initialeffluent from the gasifier/reformer (for example from a quenching stepcarried out on the gasifier effluent to remove ash and otherparticulates).

The super-atmospheric pressure at which the gaseous mixture is fed tothe first PSA system is preferably in the range of about 1-10 MPa(10-100 bar) absolute, and more preferably in the range of about 2-7 MPa(20-70 bar) absolute. The temperature of the feed will normally be inthe range of about 10-60° C., such as at about ambient temperature.However, where the first PSA system is to effect a sorption-enhancedwater-gas-shift (SEWGS) reaction then higher feed temperatures, such asin the range of about 200-500° C., would typically be required.

Where the gaseous mixture is obtained from gasification of or reformingcarbonaceous feedstock, the gasification or reforming process (and anysubsequent processing of the gasifier or reformer effluent) is thereforepreferably carried out under conditions such that the gaseous mixture isobtained at pressures and temperatures as indicated above. For example,methods of operating a gasifier such that the gasifier effluent isobtained at super-atmospheric pressures are known in the art. However,additional compression, heating and/or cooling steps may also beemployed, as and if required.

The H₂-enriched mixture, obtained from the first PSA system, is enrichedin H₂ and depleted in CO₂ relative to the gaseous mixture (i.e. the mole% of H₂ and the mole % CO₂ in the H₂-enriched mixture are greater andlesser, respectively, than those of the gaseous mixture), although someCO₂ will still be present (complete removal of CO₂ being unnecessary anduneconomic for the use of a portion of the H₂-enriched mixture as fuelfor generating power). Where the gaseous mixture also contains more oneor more other carbonaceous components, the H₂-enriched mixture may alsobe depleted in one or more, or indeed all, of said carbonaceouscomponents (i.e. the mole % of each of said components in theH₂-enriched mixture is less than that in the gaseous mixture). Where thegaseous mixture also contains H₂S, the H₂-enriched mixture is,preferably, depleted in H₂S relative to the gaseous mixture (i.e. themole % of H₂S in the H₂-enriched mixture is less than that in thegaseous mixture). Where the gaseous mixture also contains one or moreother sulphurous components, the H₂-enriched mixture is, preferably,also depleted in said sulphurous components (i.e. the mole % of each ofsaid components in the H₂-enriched mixture is less than that in thegaseous mixture).

As noted above, at least a portion of the H₂-enriched mixture from thefirst PSA is or can be used to form a fuel stream, said fuel streambeing combusted and the resulting combustion effluent expanded togenerate power. Preferably, said combustion and expansion is carried outin a gas turbine. It is therefore preferred that the H₂-enriched mixtureis sufficiently deplete in carbonaceous and sulphurous components toallow the mixture to be used for forming fuel to a gas turbine (or othersystem operated to combust the mixture and expand the resultingcombustion effluent) without requiring any further purification.

The acceptable levels of sulphurous components in the fuel stream willdepend on the allowable emission limits for SO_(x) (SO₂ and SO₃), whichwill be the final disposition of the sulphur after combustion. By way ofexample, United States Department of Energy report DOE/NETL-2007/1281,Cost and Performance Baseline for Fossil Energy Plants: Volume 1:Bituminous Coal and Natural Gas to Electricity, the disclosure of whichis incorporated herein by reference, gives examples of SO_(x) emissionallowances for an integrated gasification combined cycle (IGCC) plant(see page 35 of the report).

Likewise, any carbonaceous components other than CO₂ in the fuel streamto the gas turbine (or other combustion system) will be oxidized to CO₂,and along with CO₂ in the fuel stream will count towards the CO₂emissions from the plant, on which there will typically also beconstraints. Depending upon the regulations applicable, this could be afixed limit on the amount of CO₂ per unit of power produced, or the CO₂emissions could have an assigned monetary value (e.g. carbon tax, cap &trade) in which case the amount of CO₂ and other carbonaceous componentsin the fuel will be restricted to levels at which the power productionprocess remains economically viable.

Preferably, the first PSA system: adsorbs at least about 70%, morepreferably at least about 80% and most preferably at least about 90% ofthe CO₂ present in the gaseous mixture; and/or adsorbs at least about70%, more preferably at least about 80% and most preferably at leastabout 90% of the carbonaceous components (in total) present in thegaseous mixture. Consequently, the CO₂ recovery in the H₂-enrichedmixture (i.e. the percentage of the CO₂ present in the gaseous mixturethat is recovered in the H₂-enriched mixture) is preferably at mostabout 30%, more preferably at most about 20%, and most preferably atmost about 10%; and/or the total carbonaceous component recovery in theH₂-enriched mixture (i.e. the percentage of the carbonaceous componentsin total present in the gaseous mixture that is recovered in theH₂-enriched mixture) is preferably at most about 30%, more preferably atmost about 20%, and most preferably at most about 10%. Preferably, theH₂ recovery in the H₂-enriched mixture (i.e. the percentage of the H₂present in the gaseous mixture that is recovered in the H₂-enrichedmixture) is at least about 70%, more preferably at least about 80% andmost preferably at least about 90%. Typically, the first PSA systemadsorbs at most about 99% of the CO₂ present in the gaseous mixture, andthus the CO₂ recovery in the H₂-enriched mixture is typically at least1%.

The above percentages can be calculated from the relative molar contentsof CO₂, carbonaceous components (in total), or H₂ of the gaseous andH₂-enriched mixtures. Thus, if for example the feed of gaseous mixtureto the first PSA system were to comprise 90 kmol/hr of CO₂, 100 kmol/hrof all carbonaceous components (including CO₂) in total, and 100 kmol/hrof H₂; and the H₂-enriched mixture obtained from the first PSA systemwere to contain 9 kmol/hr of CO₂, 10 kmol/hr of all carbonaceouscomponents in total, and 90 kmol/hr of H₂; then in this case 90% of theCO₂, 90% of the carbonaceous components in total and 10% of the H₂ wouldbe adsorbed by the first PSA system, and 10% of the CO₂, 10% of thecarbonaceous components (in total) and 90% of the H₂ would be recoveredin the H₂-enriched mixture.

Where the gaseous mixture also contains H₂S and/or other sulphurouscomponents, the first PSA system, preferably, also adsorbs at leastabout 95%, more preferably at least about 99% and most preferably atleast about 99.9% of the of the total moles of sulphur in the feed.Consequently, the recovery of sulphurous components in the H₂-enrichedmixture, in terms of the total moles of sulphur in the H₂-enrichedmixture as compared to in the gaseous mixture, is preferably at mostabout 5%, more preferably at most about 1%, and most preferably at mostabout 0.1%.

Preferably, the H₂-enriched mixture comprises greater than about 90 mole% H₂. Where the gaseous mixture contains H₂S, the H₂-enriched mixturecomprises preferably less than about 50 ppm, more preferably less thanabout 20 ppm, and most preferably less than about 5 ppm H₂S.

Where water is also present in the gaseous mixture, the H₂-enrichedmixture is preferably depleted in water relative to the gaseous mixture.Preferably, the H₂-enriched mixture is substantially or entirely free ofwater. This has the advantage of allowing use of adsorbents in thesecond PSA system that are intolerant to water or perform better in a“dry” environment.

Where the gaseous mixture contains inert gases, such as N₂ and Ar, theH₂-enriched mixture will typically be enriched in these gases alongsideH₂.

The super-atmospheric pressure at which the H₂-enriched mixture isobtained is preferably the same or substantially the same as thesuper-atmospheric pressure at which the gaseous mixture is fed to thefirst PSA system. As will be explained in further detail below, theH₂-enriched mixture is formed at least in part, and preferably entirely,from gas pushed through the bed(s) of the first PSA system at thesuper-atmospheric pressure at which the gaseous mixture is fed to thefirst PSA system. In certain circumstances, some drop in pressure as thegas is pushed through the bed(s) of the PSA system may be unavoidable,in which case the pressure at which the gas is obtained will,self-evidently, be somewhat lower than that at which the gas is fed tothe first PSA system. However, preferably any such pressure drop isminimized or avoided. Where such a pressure drop does occur, thepressure drop is preferably at most 0.1 MPa (1 bar). Preferably, thefirst PSA system is operated such that the pressure at which theH₂-enriched mixture is obtained is the same as or in excess of thepressure required for being fed to the second PSA system or for formingthe fuel stream that is to be combusted in a gas turbine (or othersystem for combusting the fuel stream and expanding the resultingcombustion effluent to generate power). Where the pressures required forbeing fed to the second PSA system and for forming the fuel streamdiffer (as may often be the case), the first PSA system may, inparticular, be operated such that the pressure at which the H₂-enrichedmixture is obtained is the same as the higher or lower of these twopressures, or in between the two.

As noted above, at least a portion of the H₂-enriched mixture is or canbe fed to the second PSA system. The H₂-enriched mixture withdrawn fromthe first PSA system for feeding to the second PSA system may be feddirectly to the second PSA system as it is withdrawn, or it may be sentto an intermediate buffer/storage tank and supplied from there to thesecond PSA system. The use of a buffer/storage tank is, in particular,preferred in methods where the division of the H₂-enriched mixturebetween forming the fuel stream and being fed to the second PSA systemmay be varied, as the use of a buffer/storage tank can mitigate theeffects of such variations on the supply of H₂-enriched mixture to thesecond PSA system.

The H₂-enriched mixture may, as noted above, be obtained at a pressurethat is suitable for being fed to the second PSA system. However, wherethis is not the case, the pressure of the H₂-enriched mixture to be fedto the second PSA system may be increased or decreased as necessary, forexample using one or more compressors or expanders.

The H₂-enriched mixture may be fed to the second PSA system at thetemperature at which it is obtained from the first PSA system. Morepreferably, however, the H₂-enriched mixture fed to the second PSAsystem is cooled prior to being introduced into the second PSA system.This will typically enhance the performance of the second PSA system, asa lower feed temperature generally results in higher adsorbentcapacities. The feed to the second PSA system may be cooled via indirectheat exchange in one or more heat exchangers (using, for example, waterand/or a tail gas from the second PSA system as coolants).

As noted above, at least a portion of the H₂-enriched mixture from thefirst PSA is or can be used to form a fuel stream which is combusted andthe resulting combustion effluent expanded, preferably in a gas turbine,to generate power. The formation of this fuel stream (in its entirety orat least in part) from a gas which is already at super-atmosphericpressure reduces the amount of compression of the fuel stream neededprior to combustion and expansion, thereby increasing the efficiencywith which power is produced. As noted above, the H₂-enriched mixturemay be obtained at a super-atmospheric pressure suitable for combustionin the gas turbine (or other system used to combust the fuel stream andexpand the resulting combustion effluent to generate power) without anyfurther compression. In such circumstances, and depending on thepressures of any other gases (if any) combined with the H₂-enrichedmixture to form the fuel stream, the need for any further compression ofthe fuel stream prior to combustion and expansion may be avoidedaltogether.

The fuel stream may be formed solely from the H₂-enriched mixture.Preferably, however, the portion of the ft-enriched mixture for formingthe fuel stream is combined with a suitable diluent, such as N₂ and/orsteam, so as to reduce NO_(x) formation. The fuel stream may be heatedor cooled as required to an acceptable inlet temperature to maximisepower production (e.g. about 100-400° C.).

As noted above, in preferred embodiments the fuel stream is combustedand the resulting combustion effluent expanded in a gas turbine. As isknown in the art, a gas turbine comprises a combustion chamber in fluidflow connection with a turbine. The fuel stream to the gas turbine ismixed with a oxidant stream (e.g. air) and combusted in the combustionchamber to produce a heated combustion effluent at super-atmosphericpressure, and energy is then extracted from the combustion effluent bypassing the effluent through the turbine to generate power and anexpanded combustion effluent. The gas turbine typically furthercomprises a compressor for compressing the air (or other oxidant stream)prior to said stream entering the combustion chamber, said compressortypically being driven by the turbine (in addition to the turbinegenerating electrical power and/or power for other uses), for example bybeing connected directly to the turbine via a common drive shaft.

The H₂ product, obtained from the second PSA system, is enriched in H₂relative to the H₂-enriched mixture, and thus further enriched in H₂relative to the gaseous mixture; and is depleted in CO₂ relative to theH₂-enriched mixture, and thus further depleted in CO₂ relative to thegaseous mixture. The H₂ product is, preferably, also depleted in any andall components other than H₂ that are present in the H₂-enrichedmixture, such as any and all residual carbonaceous components(additional to CO₂), any residual sulphurous components, any remainingwater, and any inert components (e.g. Ar and N₂). Preferably, the purityof the H₂ product is such that it is suitable for use in refinery,chemical or fuel cell applications. Preferably, the H₂ product isessentially pure H₂. For example, the H₂ product preferably comprises atleast about 99.9 mole % H₂, more preferably at least about 99.99 mole %H₂. Most preferably the H₂ product comprises at least about 99.9999 mole% H₂ (i.e. wherein the combined amounts of any other components stillpresent in the product total about 1ppm or less).

H₂ product may, for example, be withdrawn and sent directly to one ormore downstream processes or for supply to a customer, or may be sent tostorage. The ability to store the H₂ product is, in particular,beneficial where the division of H₂-enriched mixture between forming thefuel stream and being fed to the second PSA system is adjustable, as theuse of storage may, in this case, mitigate the impact of variations infeed to the second PSA system. The use of storage may, for example, bedesirable or even necessary where the H₂ product is for supply to acustomer that requires a constant flow rate of high purity H₂ (and inwhich case the storage should be appropriately sized to manage theexpected variations in feed rate). The H₂ product may, for example, bestored as a gas or liquid in a tank, underground, or in the pipelinesystem (by allowing the pipeline pressure to vary).

Each of the first and second PSA systems comprises one or more beds ofadsorbent, as is known in the art. For example, each system may comprisea plurality of beds, with the PSA cycles of the individual beds beingappropriately staggered so that, at any point in time, there is alwaysat least one bed undergoing adsorption and at least one bed undergoingregeneration, such that the system can continuously separate the streamfed to it. The system may also, for example, comprise more than one bedarranged in series, with the beds in series undergoing adsorption at thesame time, the gas passing through one bed being passed to the next bedin the series, and with gases desorbed from the beds during regenerationbeing appropriately combined.

Each PSA system may comprise a single type of adsorbent, selective forall the components that are to be selectively adsorbed by said system,or more than one type of adsorbent which adsorbents in combinationprovide the desired selective adsorption. Where more than one type ofadsorbent is present, these may be intermixed and/or arranged inseparate layers/zones of a bed, or present in separate beds arranged inseries, or arranged in any other manner as appropriate and known in theart.

The first PSA system is used, as noted above, to separate theH₂-enriched mixture from the gaseous mixture, and therefore comprisesadsorbent that selectively adsorbs CO₂ (i.e. that adsorbs CO₂preferentially to H₂, or, to put it another way, that adsorbs CO₂ withgreater affinity than H₂) from the gaseous mixture at thesuper-atmospheric pressure(s) at which the gaseous mixture is fed to thefirst PSA system. Where the H₂-enriched mixture is to be also depletedin one or more other carbonaceous components, in one or more sulphurouscomponents and/or in water relative to the gaseous mixture then thefirst PSA system comprises adsorbent(s) that selectively adsorb (i.e.adsorb preferentially to H₂) these components at said pressure(s) also.Typically, the adsorbents used in the first PSA system are not selectivefor inert gases, such as N₂ and Ar, and if this is the case then wherethese gases are present in the gaseous mixture they will preferentiallypass through the first PSA system alongside H₂.

The adsorbent or adsorbents used in the first PSA system will be chosenso as to provide the desired purity of H₂-enriched mixture, and suitableadsorbents are known in the art. Examples of suitable types of adsorbentfor use in the first PSA system include aluminas, silica gels, activatedcarbons and molecular sieves. Where selective adsorption of H₂S and/orother sulphurous components is not required, a preferred adsorbent maybe activated carbon as this has a high affinity for CO₂ (and othercarbonaceous components) over H₂. Where selective adsorption of H₂Sand/or other sulphurous components is required then a preferredadsorbent would be silica gel, which has affinity and stability foradsorbing both CO₂ and H₂S, or a silica gel/carbon split. A suitabletype of silica gel for use as an adsorbent for H₂S is, for example, thehigh purity silica gel (greater than 99% SiO₂) described inUS-A1-2010/0011955, the disclosure of which is incorporated herein byreference.

If the first PSA system is to effect an SEWGS reaction (wherein the PSAsystem effects a water-gas-shift reaction at the same type as adsorbingboth existing CO₂ from the gaseous mixture and CO₂ newly formed from thegaseous mixture by the shift reaction) then the PSA system must comprisea material that is also catalytically active in terms of thewater-gas-shift reaction. A K₂CO₃ promoted hydrotalcite as described inEP-B1-1006079 and WO-A1-2010/059055, the disclosures of which areincorporated herein by reference, is a preferred material in this case.US-B2-7354562, the disclosure of which is incorporated herein byreference, describes an exemplary SEWGS process that could be carriedout by the first PSA system.

The second PSA system is used, as noted above, to separate the H₂product from the H₂-enriched mixture fed to said system, and thereforecomprises adsorbent(s) that selectively adsorbs CO₂ (i.e. that adsorbsCO₂ preferentially to H₂, or, to put it another way, that adsorbs CO₂with greater affinity than H₂), and preferably any and all componentsother than H₂ still present in the H₂-enriched mixture, at thesuper-atmospheric pressure(s) at which the H₂-enriched mixture is fed tothe second PSA system. The adsorbent or adsorbents used in the secondPSA will be chosen so as to provide the desired purity of the H₂product, and again suitable types of adsorbent are known in the art.Typically, one or more layers of adsorbent will be used, selected fromaluminas, silica gels, activated carbons and zeolite molecular sieves.In order to produce a high purity H₂ product, a silica gel/carbon/5Azeolite split may, for example, be preferred.

In circumstances where a plurality of H₂ products with differing gradesof purity are desired, the second PSA system may also be designed toproduce said plurality of H₂ products. In this case, the second PSAsystem may, for example, comprise more than one bed or sets of bedsoperated in parallel, which comprise different adsorbents and/or areoperated under different reaction conditions, so as to produce H₂products of different grades of purity.

Each of the first and second PSA systems may be operated in the same wayas known PSA systems for separating H₂ (also referred to herein asH₂-PSA systems), with all known PSA cycle options (e.g. cycle and steptimings; use, order and operation of adsorption, equalization,repressurisation, depressurization and purge steps; and so forth)appropriate to this technology area. Suitable operating conditions forPSA systems, in order to obtain H₂ purities/compositions as presentlydesired for the H₂-enriched mixture and H₂ product, are likewise knownin the art.

The PSA cycles carried out in the first and second PSA systems will, ofcourse, typically include at least adsorption, blowdown/depressurisationand purge steps. In the case of the first PSA system, during theadsorption step the gaseous mixture is fed at super-atmospheric pressureto the bed(s) undergoing the adsorption step and CO₂ (and any othercomponents of the gaseous mixture in which the H₂-enriched mixture is tobe depleted) are selectively adsorbed, the gas pushed through the bed(s)during this step forming all or at least a portion of the H₂-enrichedmixture. During the blowdown/depressurisation step(s) and purge step thepressure in the bed(s) is reduced, and a purge gas passed through thebed(s), to desorb CO₂ and other components adsorbed during the previousadsorption step, thereby regenerating the bed(s) in preparation for thenext adsorption step.

Similarly, in the case of the second PSA system, during the adsorptionstep H₂-enriched mixture is fed at super-atmospheric pressure to thebed(s) undergoing the adsorption step and CO₂ and, preferably, allcomponents other than H₂ still present in the H₂-enriched mixture areselectively adsorbed, the gas pushed through the bed(s) during this stepforming all or at least a portion of the H₂ product. During theblowdown/depressurisation step(s) and purge step the pressure in thebed(s) is reduced, and a purge gas passed through the bed(s), to desorbCO₂ and other components adsorbed during the previous adsorption step,thereby regenerating the bed(s) in preparation for the next adsorptionstep.

The preferred super-atmospheric pressures and temperatures at which thegaseous mixture and the H₂-enriched mixture are fed during theadsorption step are described above. The blowdown/depressurisation andpurge steps used in the first and second PSA systems may, for example,be conducted down to and at, respectively, about atmospheric pressure,i.e. about 0.1 MPa (1 bar) absolute, or down to and at somewhat aboveatmospheric pressure, such as in the range of about 0.1 to 0.5 MPa (1 to5 bar) absolute. Alternatively, the first and/or second PSA systemscould employ a vacuum pressure swing adsorption (VPSA) cycle, in whichcase the bed(s) of the PSA system would be depressurized down to andpurged at sub-atmospheric pressures.

Thus, in preferred embodiments, the methods of the invention furthercomprise: desorbing CO₂ from the first PSA system, at a pressure lowerthan said pressure at which CO₂ was selectively adsorbed from thegaseous mixture, to form a CO₂-enriched mixture; and desorbing CO₂ fromthe second PSA system at a pressure lower than said pressure at whichCO₂ was selectively adsorbed from the H₂-enriched mixture, to form an H₂and CO₂-containing mixture.

The CO₂-enriched mixture, also referred to herein as the first PSA tailgas, is preferably formed from the gases obtained from the first PSAsystem during the aforementioned blowdown/depressurisation and/or purgesteps of the PSA cycle. It is therefore typically obtained at about, atsomewhat above, or at below atmospheric pressure, as above described.The CO₂-enriched mixture is enriched in CO₂ relative to the gaseousmixture, but will typically contain some H₂. This is because althoughthe adsorbent in the first PSA system is, as previously noted, selectivefor CO₂ (i.e. adsorbs CO₂ preferentially to H₂) at the pressure at whichthe gaseous mixture is fed to the first PSA system, the adsorbenttypically will adsorb also some H₂ from the gaseous mixture. Inaddition, some H₂ typically will also be present in the voids, i.e. thespace in and around the adsorbent bed(s) not taken up by adsorbentmaterial, when generation of the CO₂-enriched mixture is commenced (e.g.at the start of the depressurization and/or purge step). Where theH₂-enriched mixture is also depleted in one or more other carbonaceouscomponents, in H₂S, in one or more other sulphurous components, and/orin water, then the CO₂-enriched mixture may be enriched (relative to thegaseous mixture) in one, more than one, or all such components also.Preferably, the CO₂-enriched mixture comprises at least about 70 mole %CO₂, more preferably at least about 80 mole % CO₂. The exact compositionof the CO₂-enriched mixture will depend on the process conditions underwhich it is produced, such as the pressure at which desorption iscarried out and composition of any purge gas.

The H₂ and CO₂-containing mixture, also referred to herein as the secondPSA tail gas, is preferably formed from the gases obtained from thesecond PSA system during the aforementioned blowdown/depressurisationand/or purge steps of the PSA cycle. It is therefore typically obtainedat about, at somewhat above, or at below atmospheric pressure, as abovedescribed. The H₂ and CO₂-containing mixture contains also H₂, again dueto the adsorbent in the second PSA system, although being selective forCO₂ (i.e. adsorbing CO₂ preferentially to H₂), adsorbing also some H₂from the H₂-enriched mixture, and/or due to some H₂ being present in thevoids when generation of the H₂ and CO₂-containing mixture is commenced.Indeed, although as a result of the selectivity of the adsorbent theproportion of the CO₂ present in the H₂-enriched mixture adsorbed by thesecond PSA system will be greater than the proportion of the H₂ presentin the H₂-enriched mixture adsorbed by the second PSA system, due to therelatively high content (preferably 90 mole % or more) of H₂ in theH₂-enriched mixture the actual amount of H₂ adsorbed by the second PSAsystem may be higher than the amount of CO₂ adsorbed by the second PSAsystem. The H₂ and CO₂-containing mixture may, for example, comprise atleast 40 mole % H₂ . Where, as is preferred, the H₂ product is alsodepleted in any and all components other than H₂ still present in theH₂-enriched mixture then the H₂ and CO₂-containing mixture willtypically contain these components also. The exact composition of theCO₂-containing mixture will depend on the process conditions under whichit is produced, such the pressure at which desorption is carried out andcomposition of any purge gas.

The CO₂-enriched mixture (first PSA tail gas) and H₂/CO₂-containingmixture (second PSA tail gas) may be further processed and/or used in avariety of ways.

The CO₂ from the first PSA tail gas is preferably used for enhanced oilrecovery (EOR) or geologically stored. In circumstances where the firstPSA tail gas is composed of relatively high purity CO₂, the tail gas maybe used for EOR or geologically stored without further purification. Incircumstances where the first PSA tail gas contains significant amountsof H₂, other carbonaceous components, and/or sulphurous components (suchas H₂S), further purification of the CO₂ present in the tail gas may berequired.

In particular, where the first PSA tail gas contains one or morecombustible components such as H₂, one or more combustible carbonaceouscomponents (such as CH₄ or CO) and/or one or more combustible sulphurouscomponents (such as H₂S), at least a portion of said tail gas may, forexample, be further processed by being combusted in the presence of O₂to produce a CO₂ product comprising combustion products of saidcombustible components.

The combustion product of H₂ will be water (which can be removed bycondensation or drying), the combustion product(s) of any combustiblecarbonaceous components will include CO₂ (thus providing further CO₂ forEOR or storage), and a combustion product of the combustible sulphurouscomponents will be SO_(x). Where the combustion product(s) includeSO_(x), SO_(x) may then removed from said combustion effluent by coolingthe combustion effluent to condense out water and convert SO₃ tosulfuric acid, and maintaining the cooled combustion effluent atelevated pressure(s) in the presence of O₂, water and NO for asufficient time to convert SO₂ to sulfuric acid and NO_(x) to nitricacid. The process by which SO_(x) is removed may, in particular, be asfurther described in US2007/0178035, the disclosure of which isincorporated herein by reference.

Alternatively, the first PSA tail gas may be further processed in anyother manner suitable for obtaining the desired level of CO₂ purity. Forexample, H₂S, where present, could be removed via the known Clausprocess. H₂S and/or other sulphurous components could alternatively oradditionally be removed via further adsorptive processes (using either adisposable adsorbent, or a regenerative process such as temperatureswing adsorption and/or a further PSA). CO₂ could be further separatedfrom H₂ and other, non-acid gas components (such as other carbonaceouscomponents such as CO and CH₄) via known absorptive acid gas removalprocesses. CO₂ could also be further separated from H₂ and/or othercarbonaceous components, such as CO and/or CH₄, via further PSA, viamembrane separation and/or via partial condensationprocesses.

All or a portion of the second PSA tail gas may be used to form afurther fuel stream. The further fuel stream may be used for any desiredprocess, on- or off-site. The fuel stream may, for example, be used as afuel stream for combustion to provide heat for a reformer (such as asteam-methane reformer) or gasifier used to produce the gaseous mixture,as previously described.

All or a portion of the second PSA tail gas may be further processed inthe same manner as described above for the first PSA tail gas. Thus, forexample, at least a portion of the second PSA tail gas may be combustedin the presence of O₂ to produce a CO₂ product comprising combustionproducts of H₂ and any other combustible components as may be present inthe second PSA tail gas (such as CH₄, CO and/or H₂S). Said combustionproducts can then be dealt with, if and as necessary, in the same manneras described above in relation to combustion products present in a CO₂product obtained from combusting the first PSA tail gas.

Where all or a portion of both the first PSA tail gas and the second PSAtail gas are combusted in the above manner, this could be done bycombining the first PSA tail gas and the second PSA tail gas (or aportion thereof), and then combusting the combined gases in the presenceof O₂ to produce a CO₂ product comprising combustion products of saidcombustible components. In this case the first PSA tail gas and second

PSA tail gas could share a surge/buffer tank assembly, which couldprovide for better mixing and averaging of the gas compositions andflows. Alternatively, the first PSA tail gas and second PSA tail gas (orportions thereof) could be combusted as separate streams in the samefurnace, in which case the second PSA tail gas (or portion thereof)could, for example, be combusted to provide a flame for stablecombustion of the combustible component(s) in the first PSA tail gas.Alternatively still, both the first PSA tail gas and the second PSA tailgas could be combusted in separate furnaces.

In any of these arrangements, the heat from combustion of the first PSAtail gas and/or second PSA tail gas could be used in a variety of ways.It could, for example, be used to raise the temperature of the fuelstream (i.e. the fuel stream formed from a portion or all of theH₂-enriched mixture obtained from the first PSA) prior to said fuelstream being combusted and the resulting combustion effluent expanded togenerate power. Alternatively or additionally, it could be used, forexample by being fed to an HRSG (heat recovery steam generator) system,to raise high pressure steam that is then fed to a steam turbine togenerate further power.

All or a portion of the second PSA tail gas may be compressed andrecycled to the first PSA system for further separation. This can bedone to recover further H₂ from the second PSA tail gas, and/or toseparate out further CO₂ and/or, if present, H₂S and/or any othersulphurous components. The tail gas may be recycled in a number of ways.For example all or a portion of the second PSA tail gas may be:

a) compressed to the same super-atmospheric pressure as the gaseousmixture, and added to said mixture prior to the mixture being fed to thefirst PSA system for adsorption of CO₂ and generation of the H₂-enrichedmixture.

b) compressed to the same super-atmospheric pressure as the gaseousmixture, and fed into the bed(s) of the first PSA system before or afterthe adsorption step during which the gaseous mixture is fed to thebed(s) of the first PSA system. If the mole fraction of CO₂ in thesecond PSA tail gas is greater than that in the gaseous mixture then,preferably, the tail gas is fed to the first PSA system after theadsorption step. If the mole fraction of CO₂ in the second PSA tail gasis less than that in the gaseous mixture then, preferably, the tail gasis fed to the first PSA system before the adsorption step. In eithercase, the additional gas pushed through the bed(s) of the first PSAsystem during the step of feeding the second PSA tail gas may form anadditional portion of the H₂-enriched mixture. Alternatively, the gaspushed through one bed of the first PSA system during this step may beused to repressurise another bed of the first PSA system undergoing arepressurisation step.

c) compressed to an intermediate pressure between the pressure at whichthe second PSA tail gas is obtained and the super-atmospheric pressureat which the gaseous mixture is fed to the first PSA system, and fedinto the beds of the first PSA system following a pressure equalizationstep between beds of the first PSA system. If the mole fraction of CO₂in the second PSA tail gas is greater than that in the gaseous mixturethen, preferably, the tail gas is added to a bed that decreased inpressure during the prior equalization step. If the mole fraction of CO₂in the second PSA tail gas is less than that in the gaseous mixturethen, preferably, the tail gas is added to a bed that increased inpressure during the prior equalization step. The product end of the bed(i.e. the opposite end of the bed from that to which the H₂-enrichedmixture is added during the adsorption step) may be kept closed so thatthe pressure in the bed is increased. Alternatively, the product end ofthe bed may remain connected to the bed to which it was connected to inthe prior equalization step, so that on addition of the tail gas thepressures in the two beds rise, but remain approximately equal to eachother. Alternatively still, the product end of the bed may remain openand the gas exiting from the product end may be used to purge anotherbed in the first PSA system.

All or a portion of the second PSA tail gas may be used as the purge gasor as an additional purge gas for the first PSA system. This can havethe effect of improving the performance of the first PSA system, byincreasing the dynamic capacity of the first PSA system for CO₂ andother components of the gaseous mixture that are to be selectivelyadsorbed. This use of all or a portion of the second PSA tail gas may,in particular, be preferred where CO₂ and other components for which thefirst PSA system is selective are present in relatively lowconcentrations. The purge gas may be added at the product end of thebed(s) of the first PSA system, in the manner described inFR-A1-2899890, the disclosure of which is incorporated herein byreference. Alternatively, the purge gas may be supplied to anintermediate (mid-point) position inside the bed(s) of the first PSAsystem. Where the second PSA tail gas is used as an additional purge gasthen this additional purge gas may be added before, during (as forexample described in FR-A1-2899890) or after purging with a purge gasobtained, for example, from the first PSA system itself.

A portion of the second PSA tail gas may compressed to thesuper-atmospheric pressure at which the H₂-enriched mixture is fed tothe second PSA system, and fed back into the second PSA system forfurther separation. Said portion of the tail gas may be mixed with theH₂-enriched mixture and introduced into the second PSA system as acombined mixture. Alternatively, said portion of the tail gas could beseparately introduced into the bed(s) of the second PSA system followingthe adsorption step during which the H₂-enriched mixture is introduced,and the additional gas pushed through the bed(s) of the second PSAsystem during introduction of the second PSA tail gas may form anadditional portion of the H₂ product. In either case, this will enable agreater recovery of H₂ from the second PSA, whilst increasing theconcentration of CO₂ and, preferably, any and all components of theH₂-enriched mixture other than H₂ in the tail gas. The remainingportion(s) of the second PSA tail gas may be used or processed in any ofthe other manners described herein.

All or a portion of the second PSA tail gas may be vented or flared,which may in particular be a preferred option where the amount of inertcomponents, such as N₂ or Ar, in the tail gas is relatively high. Thismay, for example, be done via “duct firing” in an HRSG. Morespecifically, all or a portion of the tail gas may be combusted, forexample in air, oxygen enriched air, or high purity oxygen, and theresulting combustion effluent combined with the expanded combustioneffluent gas obtained (via combustion and expansion, preferably in a gasturbine, as previous described) from the fuel stream formed from theH₂-enriched mixture; and the combined gases used to generate steam in anHRSG, which steam can then be expanded in a steam turbine to make power.In a combined cycle (such as in an IGCC, for example) the heat from thegas turbine flue gas is used to generate steam in a HRSG, and the steamis then supplied to a steam turbine, which expands the steam and makespower (typically electric power). By duct firing the second PSA tail gasand combining the resulting combustion effluent with the gas turbineflue gas, thereby forming a combined flue gas of increased temperature,more steam at higher temperature/pressure can be produced, resulting inmore power from the steam turbine.

All or a portion of the second PSA tail gas may be compressed and addedto the portion of the H₂-enriched mixture being used to form the fuelstream that is then (in, preferably, a gas turbine) combusted and theresulting combustion effluent expanded to generate power. If H₂S and/orother sulphurous components are present in the H₂-enriched mixture fedto the second PSA system then the second PSA tail gas will typically beenriched in these sulphurous components relative to the H₂-enrichedmixture. Where this is the case, further measures may be needed in orderto ensure that the total sulphur content of the fuel stream is suchthat, when combusted, the limits on SO_(x) emissions are not exceeded.

This may, for example, further comprise passing all or a portion of thesecond PSA tail gas through a sorbent system (for example a disposableunit comprising ZnO adsorbent) to reduce or remove any sulphurouscomponents prior to said tail gas being combined with the H₂-enrichedmixture for forming the fuel stream.

Alternatively, the first PSA system may be operated in such a mannerthat the H₂-enriched mixture obtained therefrom contains a lesserconcentration of sulphurous components than would otherwise be necessaryif said mixture were to be combusted on its own. More specifically, theconcentration of sulphurous components in the H₂-enriched mixture are inthis case sufficiently low that after said mixture has been combinedwith the second PSA tail gas the resulting fuel stream formed therefromstill has a concentration of sulphurous components that is adequate tomeet SO_(x) requirements when combusted.

In those embodiments where the division of the H₂-enriched mixturebetween forming the fuel stream and being fed to the second PSA systemis adjustable, and (when part of the H₂-enriched mixture is being fed tothe second PSA system) all or a portion of the second PSA tail gas iscompressed and added to the portion of the H₂-enriched mixture beingused to form the fuel stream, additional measures may likewise berequired to control the composition of the fuel stream when the divisionof the H₂-enriched mixture is adjusted. For example:

a) The first PSA system may be continuously operated such that thecontent of sulphurous components in the H₂-enriched mixture issufficiently low that, whatever the amount (within normal operatingparameters) of second PSA tail gas added to the H₂-enriched mixture forforming the fuel stream, combustion of the fuel stream does not lead toSO_(x) emission limits being exceeded.

b) The first PSA system may be operated such that, as the division ofthe H₂-enriched mixture is altered to increase the amount of saidmixture fed to the second PSA system (thus increasing the amount ofsecond PSA tail gas produced and incorporated into the fuel stream), theoperation of the first PSA system is altered such that amount ofsulphurous components in the H₂-enriched mixture is reduced, therebymaintaining the amount of sulphurous components in fuel stream at levelswhere SO_(x) emission limits are not exceeded. The operation of thefirst PSA system may, for example, be altered by one or more of thefollowing: (i) reducing the PSA cycle time employed in the first PSAsystem (which will reduce the concentration of H₂S in the H₂-enrichedstream, albeit at the cost of reducing also the recovery of H₂); (ii)reducing the flow rate of gaseous mixture into the first PSA system (inorder to reduce the loading of H₂S in each PSA cycle, thereby againreducing the concentration of H₂S in the H₂-enriched stream); (iii)increasing the amount of purge gas used to purge the first PSA system(again, this may reduce the concentration of H₂S in the H₂-enrichedstream, albeit at the cost of reducing also the recovery of H₂); (iv)using part of the tail gas from the second PSA as an additional purgegas for purging the first PSA system (which may increase the H₂Scapacity of the first PSA system, thereby again reducing theconcentration of H₂S in the H₂-enriched stream).

c) In the event that the adjustment of the division of the H₂-enrichedmixture results in the CO₂ content of the fuel stream changing, theamount of any N₂ added to form the fuel stream may be altered tomaintain the same gas turbine (or other combustion system) performance(in particular, as regards flame temperature).

d) If the operation of the first PSA system is altered (as discussedunder option (b) above) in response to adjustment of the division of theH₂-enriched mixture then as the content of sulphurous component in theH₂-enriched mixture decreases so may the CO₂ content. If the first PSAtail gas is treated to purify the CO₂ contained therein then a portionof this purified CO₂ may added to the H₂-enriched mixture for formingthe fuel stream, in place of or in addition to adding N₂ (as discussedunder option (c) above).

In addition to any of the above described uses, the second PSA tail gastemperature may be increased (for example prior to being otherwise usedin any of the manners described above) by being used as a coolant in oneor more heat exchangers used (as previously described) to reduce viaindirect heat exchange the temperature of the H₂-enriched mixture beingfed gas to the second PSA system.

The second PSA tail gas may be fed directly for use in any of the abovedescribed processes, or may be collected in a surge/buffer tank (forexample to allow a constant stream of gas to be removed from the tank inorder to mitigate variations in flow and pressure from the second PSAsystem).

The present invention provides, in another aspect, an apparatus forcarrying out the methods of the present invention. More particularly, anapparatus is provided for producing power and H₂ from a gaseous mixturecomprising H₂ and CO₂, the apparatus comprising:

a first pressure swing adsorption (PSA) system, comprising adsorbentthat selectively adsorbs CO₂ at super-atmospheric pressure;

a conduit arrangement for feeding at super-atmospheric pressure thegaseous mixture into the first PSA system;

a gas turbine for combusting a fuel stream and expanding the resultingcombustion effluent to generate power;

a second PSA system, comprising adsorbent that selectively adsorbs CO₂at super-atmospheric pressure;

a conduit arrangement for withdrawing at super-atmospheric pressure anH₂-enriched mixture from the first PSA system, introducing a fuel streaminto the gas turbine formed from a portion of said H₂-enriched mixture,and introducing another portion of said H₂-enriched mixture into thesecond PSA system; and

a conduit arrangement for withdrawing an H₂ product from the second PSAsystem.

In preferred embodiments, said conduit arrangement for withdrawing fromthe first PSA system the H₂-enriched mixture, introducing into the gasturbine a fuel stream formed from a portion thereof, and introducinganother portion thereof into the second PSA system, includes a valvesystem for adjustably controlling the division of the H₂ enriched streambetween the gas turbine and second PSA system.

In preferred embodiments, said valve system is adjustable between asetting whereby all the H₂ enriched mixture is sent to the gas turbineand a setting whereby all the H₂ enriched mixture is sent to the secondPSA system.

Further preferred embodiments of the apparatus will be apparent from theabove description of embodiments of the methods of the presentinvention. For example, the apparatus may further comprise one or moreheat exchangers for cooling via indirect heat exchange (using, forexample, water or second PSA tail gas as coolant) the portion ofH₂-enriched mixture to be introduced into the second PSA system. Theconduit arrangement for withdrawing H₂-enriched mixture and/or theconduit arrangement for withdrawing H₂ product may further comprise oneor more buffer/storage tanks for storing the H₂-enriched mixture and/orH₂ product in the manners discussed above. The apparatus may furthercomprise suitable conduit arrangements and systems for withdrawing andfurther processing/using first and second PSA tail gases, again inany/all of the manners discussed above.

As noted above, the methods and apparatus of the present invention, inwhich two PSA systems are used in series to separate an H₂ product fromthe gaseous mixture, with a portion of the intermediate H₂-enrichedmixture obtained at super-atmospheric pressure from the first PSA systembeing used to form a fuel stream for generating power, and in which thedivision of the H₂-enriched mixture between being used to form a fuelstream and being further separated in the second PSA system is,preferably, adjustable, provide benefits in terms of the efficiency andflexibility with which both power and a high purity H₂ product can begenerated. In particular, these methods/apparatus provide efficiencybenefits as compared to alternative arrangements that might be conceivedusing a single PSA system, two PSA systems in parallel, or two PSAsystems in series with the fuel stream being alternatively formed.

More specifically, in the methods and apparatus according to the presentinvention only the first PSA system need be designed for bulk removal ofCO₂, any other carbonaceous, and/or any sulphurous components as may bepresent in the gaseous mixture. This system can also be run at fullcapacity all the time to produce an H₂-enriched mixture of adequate (butnot unnecessarily excessive) purity of H₂ for combustion and expansionto generate power, the availability of this mixture at alreadysuper-atmospheric pressure moreover reducing compression requirementsfor the gas turbine (or other system in which the mixture is to becombusted and resulting combustion effluent expanded). The second PSAsystem need then only further purify that portion of the H₂-enrichedmixture from which the desired higher purity H₂ product is to beproduced.

Moreover, in circumstances where it is desired to alter (for whateverreason) the ratio of power to H₂ product production, this can be simplyachieved by adjusting the division of the H₂-enriched mixture betweenthe gas turbine (or other power production system) and the second PSAsystem. The second PSA system can thus be switched on and off, or rampedup and down, and the gas-turbine(s) (or other power production system)correspondingly switched off and on, or ramped down and up, to increaseH₂ product production in exchange for power production and vice-versa,as and when required and without (necessarily) adjusting the operationof the first PSA system. The use of the two PSA systems in series alsoaffords opportunities for uses of the second PSA tail gas that allowfurther integration of operation of the two PSA systems, therebyimproving overall process performance, that would not be possible usingPSA systems in parallel only.

Conversely, if a single PSA system were to be used to separate thegaseous mixture to obtain a single H₂ product (for example in the mannerdescribed in US2007/0178035), and this product were to then be split toprovide a fuel stream and a stream for refinery/chemicals/fuel cellapplications, the PSA in the system would have to be designed so thatthe H₂ product meets the minimum purity specifications for therefinery/chemicals/fuel cell applications, and as a result the purity ofthe fuel stream would likely be higher than necessary. Making higherpurity H₂ needs more adsorbent, which results in larger vessel sizes andhigher capital costs, and the adsorbent must also be purged more toremove impurities, which means a lower H₂ recovery.

Likewise, if two PSA systems were to be used in parallel to separate thegaseous mixture, with one PSA system designed and operated to provide alower purity H₂ stream for use as a fuel stream, and the other systemdesigned and operated to make a higher purity H₂ product forrefinery/chemicals/fuel cell applications, both systems would have to bedesigned and operated for bulk removal of CO₂ and any other carbonaceousor any sulphurous components to be removed from the gaseous mixture,which would again add to capital costs. The process would also be ofmore limited flexibility as regards being able to adapt to changes indemand for production of power versus high purity H₂ product. Forinstance, if it would be desired for the plant to be able to varyproduction between 100% power production and 50%/50% power and highpurity H₂ product then with two parallel PSA systems the system thatproduces an H₂ product for use as fuel will need to be sized for theamount of feed it is to receive when the plant is to be operated for100% power production. However, this PSA system will then only see halfof that feed when the plant is operated for 50%150% power and highpurity H₂ product production, vastly under-utilizing the availableadsorbent.

Finally, if (adopting an arrangement similar to that described in, forexample, U.S. Pat. No. 4,171,206) two PSA systems were to be used inseries, but all the H₂-enriched mixture obtained from the first PSAsystem fed to the second PSA system for further separation into a H₂product of suitable purity for, for example, refinery/chemicals/fuelcell applications, then either a portion of this high purity H₂ productwould have to be used for forming a fuel stream for generating power, ora portion or all of the second PSA tail gas might have to be used toform a fuel stream. Use of a portion of the high purity H₂ product as afuel stream is (as noted above in connection with the problemsassociated with using a singe PSA system) likely to be inefficient dueto such a product being of unnecessarily high H₂ purity for a fuelstream. Equally, use of the second PSA tail gas is unlikely to beoptimal, as although this may contain significant amounts of H₂ and thushave good fuel value, the gas will nevertheless inherently containincreased concentrations of carbonaceous components and (where presentin the H₂-enriched mixture) sulphurous components compared to thosepresent in the H₂-enriched mixture. Moreover, the tail gas will be atsignificantly lower pressure than the H₂-enriched mixture. Thus, use ofthe second PSA tail gas is likely to entail additional purification andcompression requirements, which will again add to operating costs.

Aspects of the invention include:

#1. A method for concurrently producing power and H₂ from a gaseousmixture comprising H₂ and CO₂, the method comprising:

feeding the gaseous mixture at super-atmospheric pressure to a firstpressure swing adsorption (PSA) system comprising adsorbent thatselectively adsorbs CO₂ at said pressure, and selectively adsorbing CO₂from the gaseous mixture with said adsorbent and at said pressure,thereby obtaining an H₂-enriched mixture at super-atmospheric pressure;

forming a fuel stream from a portion of the H₂-enriched mixture,combusting said fuel stream and expanding the resulting combustioneffluent to generate power; and

feeding another portion of the H₂-enriched mixture at super-atmosphericpressure to a second PSA system comprising adsorbent that selectivelyadsorbs CO₂ at said pressure, and selectively adsorbing CO₂ from saidportion of the H₂-enriched mixture with said adsorbent and at saidpressure, thereby obtaining an H₂ product.

#2. A method according to #1, wherein the division of H₂-enrichedmixture between forming the fuel stream and being fed to the second PSAsystem is adjustable, thereby allowing the proportion of the H₂-enrichedmixture used to form the fuel stream to be increased by reducing theproportion fed to the second PSA system, and vice-versa, without haltingthe feed of the gaseous mixture to the first PSA system.

#3. A method for adjustably producing either or both of power and H₂from a gaseous mixture comprising H₂ and CO₂, the method comprising:

feeding the gaseous mixture at super-atmospheric pressure to a firstpressure swing adsorption (PSA) system comprising adsorbent thatselectively adsorbs CO₂ at said pressure, and selectively adsorbing CO₂from the gaseous mixture with said adsorbent and at said pressure,thereby obtaining an H₂-enriched mixture at super-atmospheric pressure;and

forming either or both of a fuel stream and a PSA feed stream from theH₂-enriched mixture, the fuel stream being combusted and the resultingcombustion effluent expanded to generate power, and the PSA feed streambeing fed at super-atmospheric pressure to a second PSA systemcomprising adsorbent that selectively adsorbs CO₂ at said pressure, CO₂being selectively adsorbed from said PSA feed stream with said adsorbentand at said pressure, to thereby obtain an H₂ product;

wherein the division of H₂-enriched mixture between the fuel stream andPSA feed stream is adjustable, thereby allowing the proportion of theH₂-enriched mixture used to form the fuel stream to be increased byreducing the proportion used to form the PSA feed stream, andvice-versa, without halting the feed of the gaseous mixture to the firstPSA system.

#4. A method according to any of #1 to #3, wherein the gaseous mixturefurther comprises H₂S, and the first PSA system comprises adsorbent thatselectively adsorbs CO₂ and H₂S at the super-atmospheric pressure atwhich the gaseous mixture is fed to the first PSA system, CO₂ and H₂Sbeing selectively adsorbed from the gaseous mixture with said adsorbentand at said pressure to thereby obtain the H₂-enriched mixture.

#5. A method according to any of #1 to #4, wherein the gaseous mixturecomprises: about 30 to 75% mole % H₂; about 10 to 60% mole % CO₂; andabout 0 to 2 mole % H₂S.

#6. A method according to any of #1 to #5, wherein the gaseous mixtureis fed to the first PSA system at a pressure in the range of about 2-7MPa (20-70 bar) absolute.

#7. A method according to any of #1 to #6, wherein the CO₂ recovery inthe H₂-enriched mixture is at most about 30%, and the H₂ recovery in theH₂-enriched mixture is at least about 70%.

#8. A method according to any of #1 to #7, wherein the H₂-enrichedmixture comprises greater than about 90 mole % H₂.

#9. A method according to any of #1 to #8, wherein the H₂-enrichedmixture is obtained at a pressure which is the same or substantially thesame as the super-atmospheric pressure at which the gaseous mixture isfed to the first PSA system.

#10. A method according to any of #1 to #9, wherein the H₂-enrichedmixture fed to the second PSA system is cooled prior to being introducedinto the second PSA system.

#11. A method according to any of #1 to #10, wherein the fuel stream iscombusted and combustion effluent expanded in a gas turbine.

#12. A method according to any of #1 to #11, wherein the H₂-enrichedmixture is combined with N₂ and/or steam to form the fuel stream.

#13. A method according to any of #1 to #12, wherein the H₂ productcomprises at least about 99.9 mole % H₂.

#14. A method according to any of #1 to #13, wherein the method furthercomprises:

desorbing CO₂ from the first PSA system, at a pressure lower than saidpressure at which CO₂ was selectively adsorbed from the gaseous mixture,to form a CO₂-enriched mixture; and

desorbing CO₂ from the second PSA system, at a pressure lower than saidpressure at which CO₂ was selectively adsorbed from the H₂-enrichedmixture, to form an H₂ and CO₂-containing mixture.

#15. A method according to #14, wherein the CO₂-enriched mixturecontains one or more combustible components, and at least a portion ofsaid mixture is combusted in the presence of O₂ to produce a CO₂ productcomprising combustion products of said combustible components

#16. A method according to #14 or #15, wherein at least a portion of theH₂ and CO₂-containing mixture is combusted in the presence of O₂ toproduce a CO₂ product comprising combustion products of H₂ and any othercombustible components present in said mixture.

#17. A method according to #15 or #16, wherein the heat from combustionof said CO₂-enriched and H₂ and CO₂-containing mixtures is used to raisethe temperature of the fuel stream formed from the H₂-enriched mixture,and/or to generate steam that is fed to a steam turbine to generatefurther power.

#18. A method according to any of #14 to #17, wherein all or a portionof the H₂ and CO₂-containing mixture is compressed and recycled to thefirst PSA system for further separation.

#19. A method according to any of #14 to #18, wherein all or a portionof the H₂ and CO₂-containing mixture is used as a purge gas for thefirst PSA system.

#20. A method according to any of #14 to #19, wherein a portion of theH₂ and CO₂-containing mixture is compressed and recycled to the secondPSA system for further separation.

#21. A method according to any of #14 to #20, wherein all or a portionof the H₂ and CO₂-containing mixture is combusted, the resultingcombustion effluent combined with the expanded combustion effluentobtained from the fuel stream formed from the H₂-enriched mixture, andthe combined gases used to generate steam in a heat recovery steamgenerator.

#22. A method according to any of #14 to #21, wherein all or a portionof the H₂ and CO₂-containing mixture is compressed and added to theportion of the H₂-enriched mixture used to form the fuel stream.

#23. Apparatus for producing power and H₂ from a gaseous mixturecomprising H₂ and CO₂, the apparatus comprising:

a first pressure swing adsorption (PSA) system, comprising adsorbentthat selectively adsorbs CO₂ at super-atmospheric pressure;

a conduit arrangement for feeding at super-atmospheric pressure thegaseous mixture into the first PSA system;

a gas turbine for combusting a fuel stream and expanding the resultingcombustion effluent to generate power;

a second PSA system, comprising adsorbent that selectively adsorbs CO₂at super-atmospheric pressure;

a conduit arrangement for withdrawing at super-atmospheric pressure anH₂-enriched mixture from the first PSA system, introducing a fuel streaminto the gas turbine formed from a portion of said H₂-enriched mixture,and introducing another portion of said H₂-enriched mixture into thesecond PSA system; and

a conduit arrangement for withdrawing an H₂ product from the second PSAsystem.

#24. An apparatus according to #23, wherein said conduit arrangement forwithdrawing from the first PSA system the H₂-enriched mixture,introducing into the gas turbine a fuel stream formed from a portionthereof, and introducing another portion thereof into the second PSAsystem, includes a valve system for adjustably controlling the divisionof the H₂ enriched stream between the gas turbine and second PSA system.

#25. An apparatus according to #24, wherein said valve system isadjustable between a setting whereby all the H₂ enriched mixture is sentto the gas turbine and a setting whereby all the H₂ enriched mixture issent to the second PSA system.

Solely by way of example, certain embodiments of the invention will nowbe described with reference to the accompanying drawings.

Referring to FIG. 1, a first exemplary method according to the inventionis depicted, in which power and a high purity H₂ product areconcurrently produced from a gaseous mixture comprising a sour syngas.Sour syngas stream (1) obtained from a gasifier and water-gas-shiftreactor (not shown) is fed at super-atmospheric pressure into a firstPSA system (101) comprising adsorbent selective for CO₂ and H₂S. Thesour syngas stream comprises 60% H₂, 38% CO₂, 2% H₂S and trace amountsof N₂, Ar, CH₄ and CO. The first PSA system separates the sour syngasstream into an H₂-enriched mixture, obtained at about the samesuper-atmospheric pressure as the sour syngas stream and withdrawn asH₂-enriched stream (3), and a first PSA tail gas (2) obtained at aboutatmospheric pressure. The first PSA tail gas comprises 14% H₂, 81% CO₂and 5% H₂S. The H₂-enriched stream comprises 93% H₂, 7% CO₂, 3 ppm H₂Sand trace amounts of N₂, Ar, CH₄ and CO, which composition renders thestream suitable for use as a gas turbine fuel.

The H₂-enriched stream (3) is divided into a fuel stream (6), and a feedstream (7) to a second PSA system (102) comprising adsorbent selectivefor CO₂, H₂S, N₂, Ar, CH₄ and CO, both streams remaining of the samecomposition and at the same pressure as the H₂-enriched stream. The fuelstream is sent to one or more gas turbines (not shown) forming part ofan IGCC (not shown) where it is combusted and resulting combustioneffluent expanded in order to generate electric power. The second PSAsystem separates the feed stream (7) of H₂-enriched mixture into an H₂product stream (8), obtained at about the same super-atmosphericpressure as the feed stream (7), and a second PSA tail gas (9) obtainedat about atmospheric pressure. The second PSA tail gas comprises 59% H₂,41% CO₂, 19 ppm H₂S and trace amounts of N₂, Ar, CH₄ and CO. The H₂product stream comprises 99.99+% H₂, <1 ppm CO₂ and <1 ppb H₂S.

If a variety of different H₂ product streams were to be desired, thesecond PSA system (102) could also be composed of a set parallel PSAunits, between which the feed stream (7) would be divided, with each PSAunit making a different purity of H₂ product. Depending on the quantityof feed gas to be processed, more than one PSA unit could also berequired even if a single H₂ product is to be produced.

Referring to FIGS. 2A and 2B, a second exemplary method according to theinvention is depicted, in which in a first mode of operation (asdepicted in FIG. 2A) only power is produced from a sour sygnas, and in asecond mode of operation (as depicted in FIG. 2B) both power and a highpurity H₂ product are concurrently produced from the sour syngas. InFIGS. 2A and 2B the same reference numerals have been used as in FIG. 1to denote common features, for the sake of brevity.

Thus, as depicted in FIG. 2A, in a first mode of operation theH₂-enriched stream (3, 4) separated from the sour syngas feed (1) in thefirst PSA system (101) is used in its entirety to form a fuel stream (6)which is sent to one or more gas turbines (not shown) forming part of anIGCC (not shown) where it is combusted and the resulting combustioneffluent expanded in order to generate electric power. In this case thefuel stream (6) is formed by combining the H₂-enriched stream (3, 4)with a diluent stream (5) composed of high purity N₂.

As depicted in FIG. 2B, in the second mode the operation of the methodis adjusted so as to provide both electric power and high purity H₂.This is done by now dividing the H₂-enriched stream (3) into a stream(4) for forming the fuel stream (6) and a feed stream (7) to be sent tothe second PSA system (102), which second PSA system is now broughton-line to separate the feed stream (7) into the desired H₂ product (8)and a second PSA tail gas (9). In this mode of operation, the fuelstream (6) is then formed from combining the portion of the H₂-enrichedstream forming stream (4) with both the diluent stream (5) composed ofhigh purity N₂ and the second PSA tail gas (9).

The composition of the various streams during the first and second modesof operation are shown below in Tables 1 and 2.

As can be seen from Table 1, during the first mode of operation thefirst PSA system is operated to provide 90% CO₂ and a H₂ recovery of90%. In this embodiment, 10 ppm of H₂S is a permissible content ofsulphurous components for the gas turbine fuel.

TABLE 1 Power Production Only Stream 1 2 3 4 5 6 H₂ kmol/h 6.00E+016.00E+00 5.40E+01 5.40E+01 0.00E+00 5.40E+01 N₂ kmol/h 0.00E+00 0.00E+000.00E+00 0.00E+00 5.02E+01 5.02E+01 CO₂ kmol/h 3.80E+01 3.42E+013.80E+00 3.80E+00 0.00E+00 3.80E+00 H₂S kmol/h 2.00E+00 2.00E+001.08E−03 1.08E−03 0.00E+00 1.08E−03 H₂ % 60.00 14.22 93.42 93.42 0.0050.00 N₂ % 0.00 0.00 0.00 0.00 100.00 46.48 CO₂ % 38.00 81.04 6.57 6.570.00 3.52 H₂S ppm 20000 47369 19 19 0 10

As can be seen from Table 2, during the second mode of operation onlyhalf the amount of power (as compared to in the first mode of operation)is to be produced, and thus the fuel stream is halved (with, forexample, one of two gas turbines being switched off). The PSA cycle timeof the first PSA system is also changed such that the H₂ recoverydecreases to 85% and the CO₂ capture increases to 92.5%. This is inorder to effect also a higher level of H₂S capture by the first PSAsystem, as in this mode of operation the amount of H₂S in theH₂-enriched steam (3) must decrease from 19 ppm H₂S to 10 ppm in orderthat, after the H₂-enriched steam (3) has been combined with the secondPSA tail gas (9) and diluent stream (5), the content of H₂S in the gasturbine fuel (6) is maintained at 10 ppm H₂S. The second PSA has a H₂recovery of 85% to produce a high purity H₂ with a purity of 1 ppm ofCO₂.

TABLE 2 Production of Power and high purity H₂ 1 2 3 4 5 H2 kmol/h6.00E+01 9.00E+00 5.10E+01 2.28E+01 0.00E+00 N2 kmol/h 0.00E+00 0.00E+000.00E+00 0.00E+00 2.42E+01 CO2 kmol/h 3.80E+01 3.52E+01 2.85E+001.27E+00 0.00E+00 H2S kmol/h 2.00E+00 2.00E+00 5.40E−04 2.41E−040.00E+00 H2 % 60.00 19.50 94.71 94.71 0.00 N2 % 0.00 0.00 0.00 0.00100.00 CO2 % 38.00 76.17 5.29 5.29 0.00 H2S ppm 20000 43326 10 10 0 6 78 9 H2 kmol/h 2.70E+01 2.82E+01 2.40E+01 4.24E+00 N2 kmol/h 2.42E+010.00E+00 0.00E+00 0.00E+00 CO2 kmol/h 2.85E+00 1.58E+00 2.40E−051.58E+00 H2S kmol/h 5.40E−04 2.99E−04 0.00E+00 2.99E−04 H2 % 50.00 94.7199.9999 72.85 N2 % 44.72 0.00 0 ppm 0.00 CO2 % 5.28 5.29 1 ppm 27.14 H2Sppm 10 10 0 51

It will be appreciated that the invention is not restricted to thedetails described above with reference to the preferred embodiments butthat numerous modifications and variations can be made without departingform the spirit or scope of the invention as defined in the followingclaims.

1. A method for concurrently producing power and H₂ from a gaseousmixture comprising H₂ and CO₂, the method comprising: feeding thegaseous mixture at super-atmospheric pressure to a first pressure swingadsorption (PSA) system comprising adsorbent that selectively adsorbsCO₂ at said pressure, and selectively adsorbing CO₂ from the gaseousmixture with said adsorbent and at said pressure, thereby obtaining anH₂-enriched mixture at super-atmospheric pressure; forming a fuel streamfrom a portion of the H₂-enriched mixture, combusting said fuel streamand expanding the resulting combustion effluent to generate power; andfeeding another portion of the H₂-enriched mixture at super-atmosphericpressure to a second PSA system comprising adsorbent that selectivelyadsorbs CO₂ at said pressure, and selectively adsorbing CO₂ from saidportion of the H₂-enriched mixture with said adsorbent and at saidpressure, thereby obtaining an H₂ product.
 2. The method of claim 1,wherein the division of H₂-enriched mixture between forming the fuelstream and being fed to the second PSA system is adjustable, therebyallowing the proportion of the H₂-enriched mixture used to form the fuelstream to be increased by reducing the proportion fed to the second PSAsystem, and vice-versa, without halting the feed of the gaseous mixtureto the first PSA system.
 3. The method of claim 1, wherein the gaseousmixture further comprises H₂S, and the first PSA system comprisesadsorbent that selectively adsorbs CO₂ and H₂S at the super-atmosphericpressure at which the gaseous mixture is fed to the first PSA system,CO₂ and H₂S being selectively adsorbed from the gaseous mixture withsaid adsorbent and at said pressure to thereby obtain the H₂-enrichedmixture.
 4. The method of claim 1, wherein the gaseous mixturecomprises: about 30 to 75% mole % H₂; about 10 to 60% mole % CO₂; andabout 0 to 2 mole % H₂S.
 5. The method of claim 1, wherein the gaseousmixture is fed to the first PSA system at a pressure in the range ofabout 2-7 MPa (20-70 bar) absolute.
 6. The method of claim 1, whereinthe CO₂ recovery in the H₂-enriched mixture is at most about 30%, andthe H₂ recovery in the H₂-enriched mixture is at least about 70%.
 7. Themethod of claim 1, wherein the H₂-enriched mixture comprises greaterthan about 90 mole % H₂.
 8. The method of claim 1, wherein theH₂-enriched mixture is obtained at a pressure which is the same orsubstantially the same as the super-atmospheric pressure at which thegaseous mixture is fed to the first PSA system.
 9. The method of claim1, wherein the H₂-enriched mixture fed to the second PSA system iscooled prior to being introduced into the second PSA system.
 10. Themethod of claim 1, wherein the fuel stream is combusted and combustioneffluent expanded in a gas turbine.
 11. The method of claim 1, whereinthe H₂-enriched mixture is combined with N₂ and/or steam to form thefuel stream.
 12. The method of claim 1, wherein the H₂ product comprisesat least about 99.9 mole % H₂.
 13. The method of claim 1, wherein themethod further comprises: desorbing CO₂ from the first PSA system, at apressure lower than said pressure at which CO₂ was selectively adsorbedfrom the gaseous mixture, to form a CO₂-enriched mixture; and desorbingCO₂ from the second PSA system, at a pressure lower than said pressureat which CO₂ was selectively adsorbed from the H₂-enriched mixture, toform an H₂ and CO₂-containing mixture.
 14. The method of claim 13,wherein the CO₂-enriched mixture contains one or more combustiblecomponents, and at least a portion of said mixture is combusted in thepresence of O₂ to produce a CO₂ product comprising combustion productsof said combustible components
 15. The method of claim 14, wherein atleast a portion of the H₂ and CO₂-containing mixture is combusted in thepresence of O₂ to produce a CO₂ product comprising combustion productsof H₂ and any other combustible components present in said mixture. 16.The method of claim 15, wherein the heat from combustion of saidCO₂-enriched and H₂ and CO₂-containing mixtures is used to raise thetemperature of the fuel stream formed from the H₂-enriched mixture,and/or to generate steam that is fed to a steam turbine to generatefurther power.
 17. The method of claim 13, wherein all or a portion ofthe H₂ and CO₂-containing mixture is compressed and recycled to thefirst PSA system for further separation.
 18. The method of claim 13,wherein all or a portion of the H₂ and CO₂-containing mixture is used asa purge gas for the first PSA system.
 19. The method of claim 13,wherein a portion of the H₂ and CO₂-containing mixture is compressed andrecycled to the second PSA system for further separation.
 20. The methodof claim 13, wherein all or a portion of the H₂ and CO₂-containingmixture is combusted, the resulting combustion effluent combined withthe expanded combustion effluent obtained from the fuel stream formedfrom the H₂-enriched mixture, and the combined gases used to generatesteam in a heat recovery steam generator.
 21. The method of claim 13,wherein all or a portion of the H₂ and CO₂-containing mixture iscompressed and added to the portion of the H₂-enriched mixture used toform the fuel stream.
 22. A method for adjustably producing either orboth of power and H₂ from a gaseous mixture comprising H₂ and CO₂, themethod comprising: feeding the gaseous mixture at super-atmosphericpressure to a first pressure swing adsorption (PSA) system comprisingadsorbent that selectively adsorbs CO₂ at said pressure, and selectivelyadsorbing CO₂ from the gaseous mixture with said adsorbent and at saidpressure, thereby obtaining an H₂-enriched mixture at super-atmosphericpressure; and forming either or both of a fuel stream and a PSA feedstream from the H₂-enriched mixture, the fuel stream being combusted andthe resulting combustion effluent expanded to generate power, and thePSA feed stream being fed at super-atmospheric pressure to a second PSAsystem comprising adsorbent that selectively adsorbs CO₂ at saidpressure, CO₂ being selectively adsorbed from said PSA feed stream withsaid adsorbent and at said pressure, to thereby obtain an H₂ product;wherein the division of H₂-enriched mixture between the fuel stream andPSA feed stream is adjustable, thereby allowing the proportion of theH₂-enriched mixture used to form the fuel stream to be increased byreducing the proportion used to form the PSA feed stream, andvice-versa, without halting the feed of the gaseous mixture to the firstPSA system.
 23. Apparatus for producing power and H₂ from a gaseousmixture comprising H₂ and CO₂, the apparatus comprising: a firstpressure swing adsorption (PSA) system, comprising adsorbent thatselectively adsorbs CO₂ at super-atmospheric pressure; a conduitarrangement for feeding at super-atmospheric pressure the gaseousmixture into the first PSA system; a gas turbine for combusting a fuelstream and expanding the resulting combustion effluent to generatepower; a second PSA system, comprising adsorbent that selectivelyadsorbs CO₂ at super-atmospheric pressure; a conduit arrangement forwithdrawing at super-atmospheric pressure an H₂-enriched mixture fromthe first PSA system, introducing a fuel stream into the gas turbineformed from a portion of said H₂-enriched mixture, and introducinganother portion of said H₂-enriched mixture into the second PSA system;and a conduit arrangement for withdrawing an H₂ product from the secondPSA system.
 24. An apparatus according to claim 23, wherein said conduitarrangement for withdrawing from the first PSA system the H₂-enrichedmixture, introducing into the gas turbine a fuel stream formed from aportion thereof, and introducing another portion thereof into the secondPSA system, includes a valve system for adjustably controlling thedivision of the H₂ enriched stream between the gas turbine and secondPSA system.
 25. An apparatus according to claim 24, wherein said valvesystem is adjustable between a setting whereby all the H₂ enrichedmixture is sent to the gas turbine and a setting whereby all the H₂enriched mixture is sent to the second PSA system.